On Sun, 24 Oct 2010, besson3c wrote:
So, to paraphase this, if with these various I/O tests and tools it is determined that disks are suffering from latency issues, adding RAM or an L2ARC will help, and there is really no drawback of doing one or the other as both will be used as available. So, it's just a question of to what extent to feed the seemingly insatiable beast until it is satiated?
Zfs is just a big cache. Once the cache is large enough to hold the "working set" there should be hardly any reads to the disks.
Would it be safe to say that given the price of RAM and its performance that it would be best to start with adding RAM until it is maxed out or close to being maxed out, particularly if you have the RAM slots (as I do)?
That would depend on your budget. Given a sufficient budget, it is usually good to install lots of RAM since then the system will be fastest.
Is it also accurate to say that this is all relevant to read speeds and not write speeds? Still, by improving read speeds you'd provide ceiling room for the drives, and in doing so increase write speeds as well. Correct?
This is mostly true except that adding RAM can substantially improve write speeds as well. With sufficient RAM, overlapping writes may be coalesced (or even eliminated due to redundant writes) and the writes may be better optimized to disk layout so that the pool is more healthy and efficient. Zfs will buffer up to 30 seconds of async writes on systems with sufficiently large RAM and fast I/O.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
